It is well known in the automotive and other manufacturing industries that a length of tube can be formed to provide various cross sections and bulges along its length by placing the tube in a die set and then introducing high pressure fluid into the tube to expand the tube walls outwardly into the die cavity.
In hydroforming, as in other metal forming operations, such as stamping, it is known that residual forces will reside in the formed part and cause the formed part to spring back toward its unformed condition. Accordingly, it is well known in the design of hydroforming dies to attempt to predict the degree of springback during the die design process so that the part can be formed in a way that upon removal from the die, and the occurrence of the inevitable springback, the part will spring back to the precise finished shape that is desired.
To the extent that springback cannot be fully predicted during the design of the part and the die, it is well known that the dies must be adjusted by trimming or re-machining to relocate the die cavity so that the formed part will spring back to the desired dimension. This die operation, with the attendant trimming and re-machining of the die cavities, adds time and expense to the implementation of manufacturing processes.
The occurrence of springback is especially prevalent and difficult to predict when high strength tubular materials are to be formed.
Depending upon the complexity of the tube shape to be formed, it is often the practice to employ a tube bending operation to bend the tube about its longitudinal axis, for example, to an L-shape, so that the tube will fit into the die cavity. After the tube has gone through a tube-bending operation, certain residual forces will reside in the bent tube and these forces will become unleashed during the pressure forming in the hydroform die, further complicating the prediction of part springback and thereby further causing the need for die cavity trimming and re-machining.
In view of the foregoing, it would be highly desirable to provide a new and improved hydroforming apparatus which would minimize the time and expense of re-machining hydroforming die cavities during die tryout.